Power transmission and utility distribution systems for electricity include overhead cables carrying electricity at high tension, i.e. greater than 100 kV, etc., for distribution and transmission. Each cable is a bundle of multiple wires. A cable is two or more wires running side by side and bonded, twisted, or braided together to form a single assembly. These wires are often made from or include elemental aluminum metal and/or an aluminum alloy. Desirable performance requirements for cables for overhead power transmission applications include corrosion resistance, environmental endurance (e.g., UV and moisture), resistance to loss of strength at elevated temperatures, creep resistance, as well as relatively high elastic modulus, low density, low coefficient of thermal expansion, high electrical conductivity, and high strength. Even with high conductivity, the wires have some electrical resistance (R), which tends to increase with increasing temperature. As current passes through wires in the cable, resistance of the wires causes loss of some power (P), as heat, according to the formula P=I2R, the greater the current the more heat generated, which in turn increases resistance R.
The aluminum transmission cables are often bare or uncoated, act as conductors of electricity that operate at a high temperature, for example, approximately 60-160 degrees Celsius, and have poor emissivity. The emissivity (ϵ) is the ability of a surface to emit radiation energy compared to an ideal black body whose ϵ is defined as 1 at, the same temperature. Emissivity is expressed as a ratio of the radiation emitted by the surface to that emitted by the black body (scale is 0 to 1, with lower numbers indicating poorer emissivity. The emissivity of the uncoated aluminum wire and cable in use may be in a range of 0.05-0.10, or the like, leaving significant room for improvement of heat dissipation abilities of the cable. The hot aluminum cable has phonon vibrations that in turn cause additional Joule heating, or resistive heating.
Users of overhead utility transmission cable, e.g. power companies and public utilities, experience large energy losses caused by the cable as the operating temperature of the cable increases because resistivity of conductors generally increases with increasing temperature. This energy loss is estimated to account for billions in expenses annually through loss of generated power as it moves through the grid. For example, a typical loaded cable operates under load at a temperature up to 180 degrees Celsius. The conventional uncoated aluminum overhead utility transmission cables have energy losses through excessive Joule heating as the cable operating temperature increases. The Joule heating losses from an uncoated cable may exceed 25% of the power generated, depending on grid size. Additionally, as the temperature of aluminum cable increases, the cable also sags downward with the force of gravity which may cause a hazard. This sag phenomenon requires increasing strength of the cable, generally by including heavy steel wire in the cable's core, and the use of heavy hardware and towers to hold the wire and secure it at a safe distance to eliminate issues relating to grounding and electrically shorting out the cable. Although overhead power transmission cables including aluminum wires are known, for some applications there is a continuing desire, for example, for improved conduction efficiency.
Conventional bare cable has been previously coated using other coatings such as paints and anodizing etc., see for example WO2014025420, and cathodic plating of a dissimilar metal layer onto a metal wire; however, these coatings were limited in coverage and flexibility, showing cracking and delamination, and did not provide adhesion to the cable such that the coating had a low durability.